Is Upregulation of Sarcolipin Beneficial or Detrimental to Muscle Function?

Sarcolipin (SLN) is a regulator of sarco/endo plasmic reticulum Ca²⁺-ATPase (SERCA) pump and has been shown to be involved in muscle nonshivering thermogenesis (NST) and energy metabolism. Interestingly, SLN expression is significantly upregulated both during muscle development and in several disease states. However, the significance of altered SLN expression in muscle patho-physiology is not completely understood. We have previously shown that transgenic over-expression of SLN in skeletal muscle is not detrimental, and can promote oxidative metabolism and exercise capacity. In contrast, some studies have suggested that SLN upregulation in disease states is deleterious for muscle function and ablation of SLN can be beneficial. In this perspective article, we critically examine both published and some new data to determine the relevance of SLN expression to disease pathology. The new data presented in this paper show that SLN levels are induced in muscle during systemic bacterial (Salmonella) infection or lipopolysaccharides (LPS) treatment. We also present data showing that SLN expression is significantly upregulated in different types of muscular dystrophies including myotubular myopathy. These data taken together reveal that upregulation of SLN expression in muscle disease is progressive and increases with severity. Therefore, we suggest that increased SLN expression should not be viewed as the cause of the disease; rather, it is a compensatory response to meet the higher energy demand of the muscle. We interpret that higher SLN/SERCA ratio positively modulate cytosolic Ca²⁺ signaling pathways to promote mitochondrial biogenesis and oxidative metabolism to meet higher energy demand in muscle.

Macroinfauna responses and recovery trajectories after an oil spill differ from those following saltmarsh restoration

Given the severity of injuries to biota in coastal wetlands from the Deepwater Horizon oil spill (DWH) and the resulting availability of funding for restoration, information on impacted salt marshes and biotic development of restored marshes may both help inform marsh restoration planning in the near term and for future spills. Accordingly, we performed a meta-analysis to model a restoration trajectory of total macroinfauna density in constructed marshes (studied for ~30 y), and with a previously published restoration trajectory for amphipods, we compared these to recovery curves for total macroinfauna and amphipods from DWH impacted marshes (over 8.5 y). Total macroinfauna and amphipod densities in constructed marshes did not consistently reach equivalency with reference sites before 20 y, yet in heavily oiled marshes recovery occurred by 4.5 y post spill (although it is unlikely that macroinfaunal community composition fully recovered). These differences were probably due to initial conditions (e.g., higher initial levels of belowground organic matter in oiled marshes) that were more conducive to recovery as compared to constructed marshes. Furthermore, we found that amphipod trajectories were distinctly different in constructed and oiled marshes as densities at oiled sites exceeded that of reference sites by as much as 20x during much of the recovery period. Amphipods may have responded to the rapid increase and high biomass of benthic microalgae following the spill. These results indicate that biotic responses after an oil spill may be quantitatively different than those following restoration, even for heavily oiled marshes that were initially denuded of vegetation. Our dual trajectories for oil spill recovery and restoration development for macroinfauna should help guide restoration planning and assessment following the DWH as well as for restoration scaling for future spills.

Merkel cell carcinoma masquerading as cellulitis: a case report and review of the literature

Merkel cell carcinoma (mcc) is an uncommon malignancy of the skin arising from cells located in the deeper layers of the epidermis called Merkel cells. This malignancy rarely presents as a metastatic disease, and the field is therefore deficient in regards to management. We report the case of a 49-year-old woman who presented with a presumptive diagnosis of osteomyelitis of the left fifth digit that was resistant to treatment with antibiotics; she underwent debridement of the digit that revealed mcc and was later to have metastatic disease to her lungs, liver, and musculoskeletal system. The management of mcc, although simple in the early stage of the disease, can become challenging when it is more advanced. Multiple new modalities for its treatment have emerged over the last few years, and more recently, clinical trials are being conducted for the use of immunotherapy agents in the treatment of this malignancy.

Sarcolipin: A Key Thermogenic and Metabolic Regulator in Skeletal Muscle

Skeletal muscle constitutes ∼40% of body mass and has the capacity to play a major role as thermogenic, metabolic, and endocrine organ. In addition to shivering, muscle also contributes to nonshivering thermogenesis via futile sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA) activity. Sarcolipin (SLN), a regulator of SERCA activity in muscle, plays an important role in regulating muscle thermogenesis and metabolism. Uncoupling of SERCA by SLN increases ATP hydrolysis and heat production, and contributes to temperature homeostasis. SLN also affects whole-body metabolism and weight gain in mice, and is upregulated in various muscle diseases including muscular dystrophy, suggesting a role for SLN during increased metabolic demand. In this review we also highlight the physiological roles of skeletal muscle beyond contraction.

Cold adaptation overrides developmental regulation of sarcolipin expression in mice skeletal muscle: SOS for muscle-based thermogenesis?

Neonatal mice have a greater thermogenic need than adult mice and may require additional means of heat production, other than the established mechanism of brown adipose tissue (BAT). We and others recently discovered a novel mediator of skeletal muscle-based thermogenesis called sarcolipin (SLN) that acts by uncoupling sarcoendoplasmic reticulum Ca(2+)-ATPase (SERCA). In addition, we have shown that SLN expression is downregulated during neonatal development in rats. In this study we probed two questions: (1) is SLN expression developmentally regulated in neonatal mice?; and (2) if so, will cold adaptation override this? Our data show that SLN expression is higher during early neonatal stages and is gradually downregulated in fast twitch skeletal muscles. Interestingly, we demonstrate that cold acclimation of neonatal mice can prevent downregulation of SLN expression. This observation suggests that SLN-mediated thermogenesis can be recruited to a greater extent during extreme physiological need, in addition to BAT.

Metabolic dysfunction and altered mitochondrial dynamics in the utrophin-dystrophin deficient mouse model of duchenne muscular dystrophy

The utrophin-dystrophin deficient (DKO) mouse model has been widely used to understand the progression of Duchenne muscular dystrophy (DMD). However, it is unclear as to what extent muscle pathology affects metabolism. Therefore, the present study was focused on understanding energy expenditure in the whole animal and in isolated extensor digitorum longus (EDL) muscle and to determine changes in metabolic enzymes. Our results show that the 8 week-old DKO mice consume higher oxygen relative to activity levels. Interestingly the EDL muscle from DKO mouse consumes higher oxygen per unit integral force, generates less force and performs better in the presence of pyruvate thus mimicking a slow twitch muscle. We also found that the expression of hexokinase 1 and pyruvate kinase M2 was upregulated several fold suggesting increased glycolytic flux. Additionally, there is a dramatic increase in dynamin-related protein 1 (Drp 1) and mitofusin 2 protein levels suggesting increased mitochondrial fission and fusion, a feature associated with increased energy demand and altered mitochondrial dynamics. Collectively our studies point out that the dystrophic disease has caused significant changes in muscle metabolism. To meet the increased energetic demand, upregulation of metabolic enzymes and regulators of mitochondrial fusion and fission is observed in the dystrophic muscle. A better understanding of the metabolic demands and the accompanied alterations in the dystrophic muscle can help us design improved intervention therapies along with existing drug treatments for the DMD patients.

Sarcolipin Is a Key Determinant of the Basal Metabolic Rate, and Its Overexpression Enhances Energy Expenditure and Resistance against Diet-induced Obesity

Sarcolipin (SLN) is a novel regulator of sarcoplasmic reticulum Ca(2+) ATPase (SERCA) in muscle. SLN binding to SERCA uncouples Ca(2+) transport from ATP hydrolysis. By this mechanism, SLN promotes the futile cycling of SERCA, contributing to muscle heat production. We recently showed that SLN plays an important role in cold- and diet-induced thermogenesis. However, the detailed mechanism of how SLN regulates muscle metabolism remains unclear. In this study, we used both SLN knockout (Sln(-/-)) and skeletal muscle-specific SLN overexpression (Sln(OE)) mice to explore energy metabolism by pair feeding (fixed calories) and high-fat diet feeding (ad libitum). Our results show that, upon pair feeding, Sln(OE) mice lost weight compared with the WT, but Sln(-/-) mice gained weight. Interestingly, when fed with a high-fat diet, Sln(OE) mice consumed more calories but gained less weight and maintained a normal metabolic profile in comparison with WT and Sln(-/-) mice. We found that oxygen consumption and fatty acid oxidation were increased markedly in Sln(OE) mice. There was also an increase in both mitochondrial number and size in Sln(OE) muscle, together with increased expression of peroxisome proliferator-activated receptor δ (PPARδ) and PPAR γ coactivator 1 α (PGC1α), key transcriptional activators of mitochondrial biogenesis and enzymes involved in oxidative metabolism. These results, taken together, establish an important role for SLN in muscle metabolism and energy expenditure. On the basis of these data we propose that SLN is a novel target for enhancing whole-body energy expenditure.

Sarcolipin overexpression improves muscle energetics and reduces fatigue

Sarcolipin (SLN) is a regulator of sarcoendoplasmic reticulum calcium ATPase in skeletal muscle. Recent studies using SLN-null mice have identified SLN as a key player in muscle thermogenesis and metabolism. In this study, we exploited a SLN overexpression (Sln(OE)) mouse model to determine whether increased SLN level affected muscle contractile properties, exercise capacity/fatigue, and metabolic rate in whole animals and isolated muscle. We found that Sln(OE) mice are more resistant to fatigue and can run significantly longer distances than wild-type (WT). Studies with isolated extensor digitorum longus (EDL) muscles showed that Sln(OE) EDL produced higher twitch force than WT. The force-frequency curves were not different between WT and Sln(OE) EDLs, but at lower frequencies the pyruvate-induced potentiation of force was significantly higher in Sln(OE) EDL. SLN overexpression did not alter the twitch and force-frequency curve in isolated soleus muscle. However, during a 10-min fatigue protocol, both EDL and soleus from Sln(OE) mice fatigued significantly less than WT muscles. Interestingly, Sln(OE) muscles showed higher carnitine palmitoyl transferase-1 protein expression, which could enhance fatty acid metabolism. In addition, lactate dehydrogenase expression was higher in Sln(OE) EDL, suggesting increased glycolytic capacity. We also found an increase in store-operated calcium entry (SOCE) in isolated flexor digitorum brevis fibers of Sln(OE) compared with WT mice. These data allow us to conclude that increased SLN expression improves skeletal muscle performance during prolonged muscle activity by increasing SOCE and muscle energetics.

IKKα and alternative NF-κB regulate PGC-1β to promote oxidative muscle metabolism

Alternative NF-κB signaling modulates the activity of PGC-1β to promote oxidative metabolism in skeletal muscle.

Although the physiological basis of canonical or classical IκB kinase β (IKKβ)–nuclear factor κB (NF-κB) signaling pathway is well established, how alternative NF-κB signaling functions beyond its role in lymphoid development remains unclear. In particular, alternative NF-κB signaling has been linked with cellular metabolism, but this relationship is poorly understood. In this study, we show that mice deleted for the alternative NF-κB components IKKα or RelB have reduced mitochondrial content and function. Conversely, expressing alternative, but not classical, NF-κB pathway components in skeletal muscle stimulates mitochondrial biogenesis and specifies slow twitch fibers, suggesting that oxidative metabolism in muscle is selectively controlled by the alternative pathway. The alternative NF-κB pathway mediates this specificity by direct transcriptional activation of the mitochondrial regulator PPAR-γ coactivator 1β (PGC-1β) but not PGC-1α. Regulation of PGC-1β by IKKα/RelB also is mammalian target of rapamycin (mTOR) dependent, highlighting a cross talk between mTOR and NF-κB in muscle metabolism. Together, these data provide insight on PGC-1β regulation during skeletal myogenesis and reveal a unique function of alternative NF-κB signaling in promoting an oxidative metabolic phenotype.

Hypertension in Delhi: prevalence, awareness, treatment and control

Two cross-sectional, population-based studies were conducted to assess the prevalence, awareness, treatment and control of hypertension, among people aged 20-59 years and those over 60 years in Delhi. Study 1 (20-59 years): in total,1213 subjects from 120 clusters spread across Delhi were studied. The prevalence of hypertension was 27.5%. Of the hypertensives, 53.3% were aware of their diagnosis; 42.8% were taking treatment and only 10.5% had controlled blood pressure. About 9.0% of the hypertensives had coexisting diabetes mellitus and 8.4% were suffering from coronary disease. The prevalence of hypertension was significantly higher in urban areas, but there was no significant difference in levels of awareness, treatment and control between urban and slum areas. The prevalence of hypertension was comparable in both sexes. Women, however, were more likely to be aware of their condition. Study 2 (> or =60 years): in total,1105 subjects from 110 clusters were studied. Prevalence of hypertension was 63.8%. Isolated systolic hypertension (ISH) was found in 15.3% of the subjects. About 54% of the hypertensives were aware of their diagnosis; 43.4% were taking treatment and only 8.5% had controlled blood pressure. Prevalence of hypertension and ISH were comparable among sexes. Women were more aware and better treated. About 21.3% hypertensives had coexisting diabetes mellitus, and 14.3% were suffering from coronary disease. There was no significant difference between sexes. Urban and slum areas were also found to be comparable. Over 3% of the elderly were controlling their raised blood pressure by non-pharmacological measures. They belonged to the 'aware' category yet could not be labelled as 'hypertensives', highlighting an operational fault in the Joint National Committee definition.

Association of primary intracranial meningioma and cutaneous meningioma of external auditory canal: a case report and review of the literature

A cutaneous meningioma of the external auditory canal occurred in a 48-year-old Filipino woman who had undergone subtotal resection of a dural-based intracranial meningioma at the ipsilateral cerebellopontine angle 36 months previously. Radiologic findings demonstrated a recurrence of intracranial meningioma with surface erosion and heterogeneous densities of the mastoid bone, without extension to the area of the external auditory canal. Meningioma in the external ear canal is extremely rare. To our knowledge, there have been only two previously reported cases, both without intracranial lesion. In this case, the auditory canal lesion may represent either an ectopic meningioma arising from an arachnoid cell rest or an occult direct extension from intracranial menigioma.

How useful is immunofluorescence in tropical renal pathology?

A study of 841 renal biopsies from a south Indian hospital showed that immunofluorescence significantly helped in making a diagnosis in 74 cases. This contribution was most useful in biopsies from patients with nephritic or haematuric presentations; in those whose biopsies showed mesangial proliferative, focal proliferative, or crescentic glomerulonephritis; and in biopsies without changes detectable by light microscopy from patients with systemic lupus erythematosus.